Stephen, unless your car is unique you don't need to worry about power feeds and switches. As confirmed by Draggin, myself and the wiring schematic, the reverse light switch is already connected and provides power to the rear four way female connector when reverse is selected with ignition on.
All you need to do is pick up reverse light feed from the unused connections on this rear connector located close to existing fog light. The connections are colour coded green/brown (switched positive) and black negative. If you wish, for peace of mind a voltmeter connected to appropriate on socket will confirm they are live when reverse selected, ignition on.
How you connect your new reverse lighto is your choice. Draggin just added pins from reverse light in matching plug, which is the most elegant way. I spliced short extension into the cables near connector as I was fitting reversing light in a new pod and retaining fog light.
